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A Mixed Finite Element Approximation for Fluid Flows of Mixed Regimes in Porous Media 多孔介质中混合状态流体流动的混合有限元近似方法
IF 0.7 4区 数学 Q3 MATHEMATICS, APPLIED Pub Date : 2024-09-01 DOI: 10.1134/s096554252470074x
J. Cummings, M. Hamilton, T. Kieu

Abstract

In this paper, we consider the complex flows when all three regimes pre-Darcy, Darcy and post-Darcy may be present in different portions of a same domain. We unify all three flow regimes under mathematics formulation. We describe the flow of a single-phase fluid in ({{mathbb{R}}^{d}},;d geqslant 2) by a nonlinear degenerate system of density and momentum. A mixed finite element method is proposed for the approximation of the solution of the above system. The stabilit1y of the approximations are proved; the error estimates are derived for the numerical approximations for both continuous and discrete time procedures. The continuous dependence of numerical solutions on physical parameters are demonstrated. Experimental studies are presented regarding convergence rates and showing the dependence of the solution on the physical parameters.

摘要 在本文中,我们考虑了在同一领域的不同部分可能存在达西前、达西和达西后三种状态时的复杂流动。我们将这三种流动状态统一到数学公式中。我们通过密度和动量的非线性退化系统来描述单相流体在 ({{mathbb{R}}^{d}},;d geqslant 2) 中的流动。为近似求解上述系统,提出了一种混合有限元方法。证明了近似的稳定性;推导了连续和离散时间程序数值近似的误差估计。证明了数值解对物理参数的连续依赖性。介绍了关于收敛速率的实验研究,并显示了解对物理参数的依赖性。
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引用次数: 0
KP1-Scheme for Acceleration of Upscatter Iterations over the Neutron Thermalization Region and the Fission Source in Solving a Subcritical Boundary Value Problem KP1-在解决亚临界边界值问题时加速中子热化区和裂变源上散射迭代的方案
IF 0.7 4区 数学 Q3 MATHEMATICS, APPLIED Pub Date : 2024-09-01 DOI: 10.1134/s0965542524700672
A. M. Voloshchenko

Abstract

For the transport equation in three-dimensional (r,;vartheta ,;z) geometry, a (K{{P}_{1}})-scheme is constructed for accelerating the convergence of upscatter iterations over the neutron thermalization region and the fission source in solving a subcritical boundary value problem, consistent with the Weighted Diamond Differencing (WDD) scheme, and its generalization to the case of nodal Linear Discontinues (LD) and Linear Best (LB) schemes of the 3rd and 4th order of accuracy in spatial variables is considered. To solve the system for accelerating corrections, an algorithm based on the use of the cyclic splitting method was used, similar to that used earlier when constructing the (K{{P}_{1}})-scheme for accelerating the convergence of inner iterations. An algorithm for determining the energy dependence for accelerating corrections of the (K{{P}_{1}})-scheme for accelerating the convergence of upscatter iterations is considered. The choice of a criterion for the convergence of upscatter iterations is considered, and a criterion integral over up-scattered thermal neutrons for the convergence of upscatter iterations over the region of neutron thermalization is proposed. A modification of the algorithm for the case of three-dimensional (x,;y,;z) geometry is considered. Numerical examples of using the (K{{P}_{1}})-scheme for accelerating the convergence of upscatter iterations to solve typical problems of neutron transport in three-dimensional geometry are given.

AbstractFor the transport equation in three-dimensional (r,;vartheta ,. z) geometry;z)几何中的输运方程,构建了一种与加权菱形微分(WDD)方案相一致的用于加速中子热化区和裂变源上散射迭代收敛的(K{{P}_{1}})方案,并考虑了将其推广到空间变量精度为3阶和4阶的节点线性不连续(LD)和线性最佳(LB)方案的情况。为了求解加速修正系统,使用了一种基于循环分裂法的算法,类似于之前构建 (K{{P}_{1}}) 方案以加速内部迭代收敛时使用的算法。研究考虑了一种算法,用于确定加速上散射迭代收敛的(K{{P}_{1}})方案加速修正的能量依赖性。考虑了上散射迭代收敛标准的选择,并提出了中子热化区域上散射热中子迭代收敛的标准积分。考虑了针对三维 (x,;y,;z) 几何形状的算法修改。给出了使用 (K{{P}_{1}}) 方案加速上散射迭代收敛以解决三维几何中子输运典型问题的数值示例。
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引用次数: 0
Hamiltonian System for Three-Dimensional Problem of Two-Dimensional Decagonal Piezoelectric Quasicrystals and Its Symplectic Analytical Solutions 二维十边形压电准晶体三维问题的哈密顿体系及其交点解析解
IF 0.7 4区 数学 Q3 MATHEMATICS, APPLIED Pub Date : 2024-09-01 DOI: 10.1134/s0965542524700763
Zhiqiang Sun, Guolin Hou, Yanfen Qiao, Jincun Liu

Abstract

A Hamiltonian system is developed for the three-dimensional (3D) problem of two-dimensional (2D) decagonal piezoelectric quasicrystals via the variational principle. Based on the full state vector and the properties of the Hamiltonian operator matrix, the superposition principle of solutions obtains the symplectic analytical solutions of the problem under simply supported boundary conditions. Numerical examples are illustrated to display the effects of the stacking sequences and material constants on the stresses, displacements, electric potential, and electric displacements under the mechanical and electric displacement loadings. The symplectic analytical solutions presented in the article can be used as a reference for further numerical research.

摘要 通过变分原理为二维十边形压电准晶体的三维(3D)问题建立了哈密顿体系。基于全状态矢量和哈密顿算子矩阵的性质,利用解的叠加原理得到了该问题在简单支撑边界条件下的交点解析解。数值示例展示了堆叠序列和材料常数在机械和电位移载荷下对应力、位移、电动势和电位移的影响。文章中给出的折中分析解可作为进一步数值研究的参考。
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引用次数: 0
On the Uniqueness of Determining the Mesh Fundamental Solution of Laplace’s Equation in the Theory of Discrete Potential 论离散势理论中确定拉普拉斯方程网格基本解的唯一性
IF 0.7 4区 数学 Q3 MATHEMATICS, APPLIED Pub Date : 2024-09-01 DOI: 10.1134/s0965542524700696
I. E. Stepanova, I. I. Kolotov, A. G. Yagola, A. N. Levashov

Abstract

The paper examines the problem of unique determination of the fundamental solution of a mesh analogue of Laplace’s equation within the theory of discrete gravitational potential. The mesh fundamental solution of the finite-difference analogue of Laplace’s equation plays a key role in reconstructing a continuously distributed source of gravitational or magnetic field from heterogeneous and different-precision data obtained at points of a certain mesh set.

摘要 本文研究了离散重力势理论中拉普拉斯方程网格模拟基本解的唯一确定问题。拉普拉斯方程的有限差分模拟的网格基本解在从某一网格集各点获得的异质和不同精度的数据重建连续分布的引力场或磁场源方面起着关键作用。
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引用次数: 0
Numerical Diagnostics of Solution Blow-Up in a Thermoelectric Semiconductor Model 热电半导体模型中溶液炸裂的数值诊断
IF 0.7 4区 数学 Q3 MATHEMATICS, APPLIED Pub Date : 2024-09-01 DOI: 10.1134/s0965542524700647
M. O. Korpusov, R. S. Shafir, A. K. Matveeva

Abstract

A system of equations with nonlinearity in the electric field potential and temperature is proposed for describing the heating of semiconductor elements on an electrical board with thermal and electrical breakdowns possibly arising over time. A method for numerical diagnostics of solution blow-up is considered. In the numerical analysis of the problem, the original system of partial differential equations is reduced to a differential-algebraic system, which is solved using a single-stage Rosenbrock scheme with complex coefficients. The blow-up of the exact solution is detected using an asymptotically sharp a posteriori error estimate obtained by computing approximate solutions on sequentially refined grids. The blow-up time is numerically estimated in the case of various initial conditions.

摘要 提出了一个电场势能和温度非线性方程组,用于描述电路板上半导体元件的加热情况,随着时间的推移可能会出现热和电气故障。研究还考虑了一种解炸裂的数值诊断方法。在对问题进行数值分析时,将原始偏微分方程系统简化为微分代数系统,并使用具有复系数的单级 Rosenbrock 方案进行求解。通过在连续细化的网格上计算近似解获得渐近尖锐的后验误差估计,从而检测精确解的膨胀。在各种初始条件下,对炸毁时间进行了数值估算。
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引用次数: 0
On the Uniform Convergence of Approximations to the Tangential and Normal Derivatives of the Single-Layer Potential Near the Boundary of a Two-Dimensional Domain 论二维域边界附近单层势切线和法线导数近似值的均匀收敛性
IF 0.7 4区 数学 Q3 MATHEMATICS, APPLIED Pub Date : 2024-09-01 DOI: 10.1134/s0965542524700623
D. Yu. Ivanov

Abstract

Semi-analytical approximations to the tangential derivative (TD) and normal derivative (ND) of the single-layer potential (SLP) near the boundary of a two-dimensional domain, within the framework of the collocation boundary element method and not requiring approximation of the coordinate functions of the boundary, are proposed. To obtain approximations, analytical integration over the smooth component of the distance function and a special additive-multiplicative method for separation of singularities are used. It is proved that such approximations have a more uniform convergence near the domain boundary compared to similar approximations of the TD and ND of SLP based on a simple multiplicative method of separation of singularities. One of the reasons for the highly nonuniform convergence of traditional approximations to TD and ND of SLP based on the Gaussian quadrature formulas is established.

摘要 在配位边界元法框架内,提出了二维域边界附近单层势(SLP)切向导数(TD)和法向导数(ND)的半解析近似值,不需要对边界坐标函数进行近似。为了获得近似值,使用了距离函数平滑分量的解析积分法和一种特殊的奇异点分离加乘法。事实证明,与基于简单的奇点分离乘法的 SLP TD 和 ND 近似值相比,这种近似值在域边界附近具有更均匀的收敛性。基于高斯正交公式的传统 SLP TD 和 ND 近似值收敛性极不均匀的原因之一已经确定。
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引用次数: 0
Generalization of the Method of Scattering Matrices to Problems in Nonlinear Dispersion Media 将散射矩阵法推广到非线性弥散介质问题中
IF 0.7 4区 数学 Q3 MATHEMATICS, APPLIED Pub Date : 2024-09-01 DOI: 10.1134/s0965542524700660
A. A. Belov, Zh. O. Dombrovskaya

Abstract

In recent years, much attention has been paid to integrated photonics devices based on nonlinear media. A generalization of the transfer matrix method to problems in plane-parallel layered media with quadratic and cubic nonlinearity is proposed. The incident radiation can be either a monochromatic wave or a non-monochromatic pulse. Previously, such problems could only be solved using grid methods. The proposed approaches significantly expand the range of applicability of matrix methods and are drastically superior in efficiency to the well-known grid methods.

摘要 近年来,基于非线性介质的集成光子器件备受关注。本文提出了将传递矩阵法推广到具有二次方和三次方非线性的平面平行层状介质中的问题。入射辐射可以是单色波,也可以是非单色脉冲。以前,这类问题只能用网格方法求解。所提出的方法大大扩展了矩阵方法的适用范围,在效率上大大优于众所周知的网格方法。
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引用次数: 0
The MDM Algorithm and the Sylvester Problem MDM 算法和希尔维斯特问题
IF 0.7 4区 数学 Q3 MATHEMATICS, APPLIED Pub Date : 2024-09-01 DOI: 10.1134/s0965542524700684
V. N. Malozemov, N. A. Solov’eva, G. Sh. Tamasyan

Abstract

When developing numerical methods for solving nonlinear minimax problems, the following auxiliary problem arose: in the convex hull of a certain finite set in Euclidean space, find a point that has the smallest norm. In 1971, B. Mitchell, V. Demyanov and V. Malozemov proposed a non-standard algorithm for solving this problem, which was later called the MDM algorithm (based on the first letters of the authors' last names). This article considers a specific minimax problem: finding the smallest volume ball containing a given finite set of points. It is called the Sylvester problem and is a special case of the problem about the Chebyshev center of a set. The Sylvester problem is associated with a convex quadratic programming problem with simplex constraints. To solve this problem, it is proposed to use a variant of the MDM algorithm. With its help, a minimizing sequence of feasible solutions is constructed such that two consecutive feasible solutions differ in only two components. The indices of these components are selected based on certain optimality conditions. We prove the weak convergence of the resulting sequence of feasible solutions that implies that the corresponding sequence of vectors converges in norm to a unique solution to the Sylvester problem. Four typical examples on a plane are given.

摘要在开发解决非线性最小问题的数值方法时,出现了以下辅助问题:在欧几里得空间中某个有限集合的凸壳中,找到一个具有最小规范的点。1971 年,B. Mitchell、V. Demyanov 和 V. Malozemov 提出了解决这一问题的非标准算法,后来被称为 MDM 算法(基于作者姓氏的第一个字母)。本文考虑的是一个特定的 minimax 问题:寻找包含给定有限点集的最小体积球。它被称为西尔维斯特问题,是关于集合的切比雪夫中心问题的一个特例。西尔维斯特问题与带有单纯形约束的凸二次编程问题相关联。为了解决这个问题,建议使用 MDM 算法的变体。在该算法的帮助下,可以构建一个可行解的最小化序列,使得两个连续的可行解只有两个部分不同。这些分量的指数是根据某些最优条件选择的。我们证明了所得到的可行解序列的弱收敛性,这意味着相应的向量序列在规范上收敛于西尔维斯特问题的唯一解。我们给出了平面上的四个典型例子。
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引用次数: 0
Regularization of the Solution to Degenerate Systems of Algebraic Equations Exemplified by Identification of the Virial Equation of State of a Real Gas 以识别实气体的室温状态方程为例,对代数方程的退化系统求解进行正则化处理
IF 0.7 4区 数学 Q3 MATHEMATICS, APPLIED Pub Date : 2024-09-01 DOI: 10.1134/s096554252470060x
A. G. Vikulov

Abstract

Thermodynamic calculation of a cycle in a two-phase region requires an equation of state of the working medium, which is used as a virial equation with unknown temperature functions. A degenerate system of algebraic equations has been constructed for unknown coefficients, which are the values of virial functions on a temperature mesh. Based on the regularization method, a variational-iterative algorithm for solving a degenerate system of equations has been developed. A computational experiment to confirm the effectiveness of the method was carried out.

摘要两相区循环的热力学计算需要工作介质的状态方程,该方程被用作带有未知温度函数的病毒式方程。针对未知系数,即温度网格上的病毒式函数值,构建了一个退化代数方程系统。基于正则化方法,开发了一种求解退化方程组的变分迭代算法。为证实该方法的有效性,进行了计算实验。
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引用次数: 0
Application of Universal Fast Trigonometric Interpolation and Extrapolation for Determining the Launch Point Coordinates of a Flight Vehicle 应用通用快速三角内插法和外推法确定飞行器发射点坐标
IF 0.7 4区 数学 Q3 MATHEMATICS, APPLIED Pub Date : 2024-09-01 DOI: 10.1134/s0965542524700702
A. D. Chernyshov, O. Yu. Nikiforova, V. V. Goryainov, I. G. Rukin

Abstract

The foundations of fast universal trigonometric interpolation for nonperiodic functions used to obtain high-accuracy approximate solutions are described. High-accuracy formulas are derived for computing the launch point coordinates of a flight vehicle by applying universal fast trigonometric interpolation combined with extrapolation at the endpoints of a given interval. Numerical experiments show that, after launching the first vehicle, the launch point coordinates can be determined in 7 s with accuracy of ({{10}^{{ - 17}}}) m.

摘要 阐述了用于获得高精度近似解的非周期性函数快速通用三角插值法的基础。通过在给定区间的端点应用通用快速三角内插法结合外推法计算飞行器的发射点坐标,得出了高精度公式。数值实验表明,在发射第一个飞行器后,可以在 7 秒内确定发射点坐标,精度为 ({{10}^{ - 17}}}) m。
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引用次数: 0
期刊
Computational Mathematics and Mathematical Physics
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